In January 2019 COMEAP published a report into the potential for adverse health effects from travel on London Underground. The report concluded that ‘Much work is still needed to understand the relationship between subway PM exposure and any health effects’ and listed, among its recommendations, an:

‘investigation of ways to increase the usefulness of employment health records of those working in the underground to assess potential adverse health effects of underground exposures.’

The Committee noted that such research will require collaboration across disciplines, including epidemiology, toxicology and atmospheric chemistry. 

This project meets the above criteria and involves two studies:

Study 1: the short-term, adverse health impacts of working on the Underground; a retrospective cohort study of sickness absence

We will examine rates of sickness absence in TfL staff over the past five years and relate these to contemporary measures of exposure to Underground dust. To do this we will:

 1. Identify all (or relevant) TfL workers in employment from 2014 onwards

2. Allocate them to contemporary exposure categories

3. Collate, from electronic records, sickness absence data for each: date/cause/duration of each spell

4. Calculate rates of cause-specific absence per person-months by exposure category

Study 2: the long-term, adverse health impacts of working on the Underground; a retrospective cohort analysis of mortality

This more ambitious study will take advantage of the high-quality employment records held by LU (Pension Fund). Employment at LU, by job title and duration, will be assigned level(s) of dust exposure and subsequently linked to national, cause-specific mortality records. To achieve this we will:

1. Acquire permission to link employee data to mortality data

2. Identify all (or relevant) workers in employment from as far back as possible

3. Link each to ONS mortality data

4. Allocate them to categories that reflect their era-dependent exposures;

5. Undertake historical exposure assessment for each category

6. Estimate cumulative exposures for each individual

7. Calculate cause-specific standardised mortality ratios for each exposure category

Estimating historical concentrations of job-specific exposures will be undertaken by comparing current modelled concentrations (above) to previous occupational health measurements to derive scaling factors to adjust for any observed trend in concentrations. Further adjustments will also need to be made for size fraction and measurement methodology.

PI:  Dr Dave Green